1. Field of the Invention
Ultrasound imaging is utilized for real-time, noninvasive, nondestructive assessment of material density and strength of hard tissue to determine complex three-dimensional shapes, surface topology, non-uniform internal structures and to determine material properties of tissues.
The present invention combines a Low Intensity Pulsed Ultrasound (LIPUS) device with a surface topology mapping apparatus to provide focused ultrasound therapy to enhance healing and accelerate callus mineralization.
2. Brief Description of the Background Art
Osteoporosis and osteopenia are common diseases affecting a large proportion of the population, mostly elderly, which increase the risk of fracture at critical skeletal sites, e.g., hip, wrist and spine. After fracture, healing complications include non-union and poor quality of life. Various remedies have been developed to treat delayed unions and non-unions.
Ultrasound (US) is known to have a strong positive influence on the three key stages of the healing process: inflammation, repair, and remodeling, due to the enhancement by US of angiogenic, chondrogenic and osteogenic activity. Clinical evidence confirms that US can effectively treat delayed unions and non-unions.
US therapy applied to fracture healing relates to differential energy absorption of ultrasound that gives rise to an acoustic streaming, and resultant fluid flow as a mechano-transduction signal. Low energy mechanical stimulation, e.g. low intensity pulsed ultrasound (LIPUS), accelerates healing of bone fractures and other recovery. See, U.S. Patent Publication 2008/0021327 A1 of Ahmed El-Bialy, the contents of which are incorporated herein by reference. LIPUS stimulation transmits mechanical energy through and into biological tissues as an acoustic pressure wave and has been widely used in medicine as a non-invasive therapeutic tool, showing an accelerated rate of healing of fresh fractures.
LIPUS stimulation can assist non-union and accelerate fracture repair. However, the effectiveness of localized LIPUS with optimized intensity has not been fully investigated. Moreover, soft tissue and cortical shell interference limits use of LIPUS stimulation.
LIPUS is a biophysical form of intervention in the fracture-repair process, which through several mechanisms accelerates healing of fresh fractures and enhances callus formation in delayed union and nonunion. The acoustic pressure wave induced by US is indicative of a mechanical signal that takes full advantage of bone tissue sensitivity to low-level physical signals. However, such acoustically driven mechanical signal is several orders of magnitude lower than the peak strains generated by functional load-bearing, while the rates of loading induced by the US are several orders of magnitude higher. Extremely low-level, high-frequency mechanical signals persist in functionally loaded bone and represent strong regulatory signals to skeletal tissue, even during fracture-healing.
Therapeutic US, and some operative US, uses intensities as high as 1 to 30 W/cm2 and can cause considerable heating in living tissues. The use of US as a surgical instrument involves even higher levels of intensity (5 to 300 W/cm2), and sharp bursts of energy used to fragment calculi initiate the healing of non-unions, ablate diseased tissues such as cataracts, and even remove methylmethacrylate cement during revision of prosthetic joints. The intensity level used for imaging, which is five orders of magnitude below that used for surgery, is regarded as non-thermal and nondestructive. Current therapeutic US uses plane waves and exposes the energy to broad range of tissues. The radical changes in density inherent in a healing callus may lose significant amounts of energy in the pathway of ultrasound. A localized and targeted/guided exposure of LIPUS overcomes these limitations and dramatically increases the efficiency of the treatment. The combined diagnostic and therapeutic quantitative ultrasound (QUS) with focal scan as in the present invention overcomes such shortcomings.
In the present invention, focused LIPUS of modified LIPUS (mLIPUS) acts as an alternating pressure wave, creating localized pressure gradients within micro porosities of the subject bone, and anabolic shear forces on cell membranes, thereby changing local solute concentrations and initiating local fluid flow exchange/interaction. In vitro studies show that mLIPUS enhances osteoblast proliferation and endochondral bone formation and in vivo studies show mLIPUS to be anabolic in fresh fractures, enhancing endochondral bone formation, mineral density and mechanical strength.
The present invention combines ultrasound focusing and mLIPUS stimulation to provide early identification of bone disorder and accelerate localized fracture healing.